The present invention relates to a method for recording information on an integrated type of information recording system comprising a photoelectric sensor and a liquid crystal recording medium stacked on each other.
There has so far been known an integrated type of information recording system which comprises a liquid crystal recording medium including on an electrode a liquid crystal-polymer composite layer with polymer balls filled in a liquid crystal phase and a photoelectric sensor including a photoconductive layer on an electrode layer, both stacked on each other, and which is exposed to light at an applied voltage to record an image thereon.
Such an integrated type of information recording system is schematically shown in FIG. 1. More specifically, this system is broken down into two types, the first type wherein a liquid crystal medium 20 is directly stacked on a photoelectric sensor 10 as shown in FIG. 1(a), and the second type wherein an interlayer 24 made up of a transparent dielectric material (transmission type) or a dielectric mirror (reflection type) is interposed between them, as shown in FIG. 1(b). In the photoelectric sensor 10 a transparent electrode 12 and a photoconductive layer 13 are successively stacked on a transparent substrate 11, and in the liquid crystal recording medium 20 a liquid crystal-polymer composite layer 23 is stacked on a transparent electrode 22. When the photoconductive layer 13 used has a single-layer structure, amorphous selenium, amorphous silicon and so on may be used in the form of an inorganic photoconductive layer, and polyvinyl carbazole may be used with trinitrofluorenone added thereto in the form of an organic photoconductive layer. Alternatively, use may also be made of a composite photoconductive layer comprising a carrier generation layer having an azo dye dispersed in resin such as polyvinyl butyral and a carrier transport layer having a hydrazone derivative mixed with resin such as polycarbonate, both layers stacked on each other.
When such an integrated type of information recording system is irradiated with recording light in the form of visible light with voltage applied from a power source 30 across the electrodes 12 and 22 thereof, as shown in FIG. 2, there is a change in the conductivity of the photoconductive layer 13 depending on the intensity of visible light. This change in turn causes an electric field applied on the liquid crystal layer 23 to change, resulting in a change in the orientation of liquid crystals. Even after removal of the electric field by putting off the application of voltage, this state is so maintained that image information can be recorded.
To read out the thus recorded image information, the liquid crystal recording medium 20 is irradiated with reading light which emanates from a light source 60 and is selected in terms of wavelength through a filter 70, as shown in FIG. 3(a) (transmission type) and FIG. 3(b) (reflection type). The incident light is modulated by the orientation of liquid crystals in the liquid crystal recording medium, while the transmitted (or reflected) light is converted by an photoelectric converter 80 into an electrical signal, which may be outputted through a printer or CRT, if required. The light source 60 used may be a white light source such as a xenon or halogen lamp, or laser light.
However, a problem with recording an image with an integrated type of liquid crystal recording system is that, although depending on the characteristics of the photoelectric sensor, the quantity of exposure light (light intensity.times.exposure time) required for image recording often becomes too large, or no image can be recorded at all. A liquid crystal recording layer has a certain threshold voltage. As can be understood from FIG. 4 illustrating the range of modulation of liquid crystals, when the voltage applied on the liquid crystal layer is within the range of 200 V to 250 V for example, recording can be made depending on the quantity of exposure light. At lower than 200 V, however, no image can be recorded because the liquid crystals are hardly oriented. At higher than 250 V, no image can again be recorded because of saturated orientation.